NASHVILLE, TENN. — Potassium management is not always as simple as replacing what the crop removes.
Nutrien Ekonomics explains the difference between rebuilding and maintaining soil potassium, and what each approach means for long-term fertility planning.
Rebuilding and maintaining soil potassium levels are two strategies farmers can use to ensure overall soil fertility with respect to potassium.
If you’re building soil potassium, you need to apply potassium fertilizer above what you’re removing with the harvested crop.
If you’re simply maintaining your potassium levels, you only need to apply as much fertilizer as you’re taking off in the harvested crop.
Either way, you need a couple of pieces of information: your soil test and your crop nutrient removal values from your expected harvest for potassium.
Growers should rebuild potassium levels when their soil sample says they are running low on nutrients. Typically, this is a value below the established critical value for a state or province. It shows up as the very low or low category on the soil test.
These are great times to invest in potassium nutrients and, over time, push your soil values back over that critical value.
By rebuilding those stocks, maintenance levels become important when you are above that critical value.
You have some potassium in the savings account. You can typically draw that down with respect to the nutrient removal in the crop, and then you just need to know how much the crop takes off and how much you need to put back in subsequent fertilizer applications.
One misconception about rebuilding soil fertility is that you have to do it all in one season.
You don’t.
You can take a four- to five-year approach. This helps you spread your costs and logistics out over time, so rebuilding is more of a slow ramp than it is all in one shot in one season.
Many growers typically get on a four- to five-year rebuilding plan.
First, determine the need. Have your soil test in front of you and know how short of potassium the soil is. University recommendations can help determine what is needed to get back above the critical value.
Then, divide that amount out over the number of years you want the program to run.
Most growers are on a four- to five-year program, which helps with logistics and costs.
If you were short on potassium in your soil samples and they were coming back very low to low, you can build that potassium back up by applying more fertilizer than you are taking off in the harvested crop.
Once you are above the critical value, you can go into maintenance mode.
That is where you are trying to maintain your soil levels at a stable level above the critical value.
You can plan for that by taking your yield numbers and putting them into a crop nutrient removal calculator and calculating the pounds per acre of K2O that left the field.
That is what you put back on in your fertilizer application.
